Final answer:
Glycerol is the cryoprotectant from the provided options. It prevents ice crystal damage during cryopreservation, unlike isotonic saline or media like RPMI and TSB which are not cryoprotectants.
Step-by-step explanation:
The cryoprotectant among the options provided is glycerol. Cryoprotectants are substances used to protect biological tissue from freezing damage due to ice formation during cryopreservation. For cells being preserved at very low temperatures, such as in liquid nitrogen, cryoprotectants help prevent ice crystal formation which can damage the cell membrane and internal structures.
Glycerol is a common cryoprotectant used in cell cryopreservation because it penetrates cell membranes and reduces ice formation during freezing. Isotonic saline, while used in medical treatments, is not a cryoprotectant; it is designed to match the osmotic pressure of blood. Roswell Park Memorial Institute (RPMI) and Trypticase Soy Broth (TSB) are both used in laboratory settings for growing and maintaining cell cultures but do not serve as cryoprotectants.